BRAKING DEVICE FOR ELEVATOR HOIST TECHNICAL FIELD [0001] The present invention relates to a braking device that is provided to a hoist for driving an elevator. BACKGROUND ART [0002] A braking device for an elevator hoist of the related art adopts an internal expansion direct-acting electromagnetic brake, as disclosed in Patent Document 1. According to the braking device, a fixed iron core and a movable iron core are provided in a drum, a brake shoe is attached to the movable iron core via two coupling members, and the coupling members are screw-threaded in screw holes of the movable iron core so that they can be moved forward-and-backward and be adjusted in a screw manner, and are fixed with lock nuts. The braking device is adapted to press and separate a frictional member of the brake shoe to and from an inner peripheral surface of the drum, thereby braking and opening the drum. According to the braking device, a gap that is formed when the frictional member and the drum are separated is adjusted by adjusting protruding lengths of the coupling members from the movable iron core. RELATED TECHNICAL DOCUMENTS PATENT DOCUMENTS [0003] Patent Document 1: JP 2002-284486A (page 6 and FIG. 2) SUMMARY OF THE PRESENT INVENTION PROBLEMS TO BE SOLVED [0004] However, according to the above braking device, when adjusting the gap in the routine maintenance, a maintenance-man measures the gap between the frictional member and the drum of the braking device. Then, when the measured gap deviates from a prescribed value, the maintenance-man loosens the lock nuts of the coupling members,and then the respective coupling members is moved forward-and-backward in a screw manner so that the gap belongs to the prescribed value, thereby adjusting the protruding lengths of the coupling members from the movable iron core. At this time, the maintenance-man adjusts the lengths of the coupling members so that the gap is substantially uniform. Accordingly, the gap adjustment is troublesome and requires much time. [0005] The present invention has been made to solve the above problem. An object of the present invention is to provide a braking device for an elevator hoist capable of easily adjusting a gap between a frictional member and a drum. MEANS FOR SOLVING THE PROBLEMS [0006] A braking device of an elevator hoist of the present invention includes a housing that accommodates a rotatable drum therein and has an opening section having one end and other end opened; a pivoting member that is pivotably provided to the one end of the opening section and has the other end opened; a fastening and releasing member that fastens and releases the other end of the pivoting member to and from the other end of the opening section; an adjusting unit that adjusts a distance between the other end of the pivoting member and the other end of the opening section, with being fastened to the pivoting member; a braking section that is provided to the pivoting member and presses the drum, and a braking drive unit that is provided to the pivoting member and is pressed and separated to and from an outer peripheral surface of the drum. [0007] According to the present invention, in a state in which the fastening and releasing member fastened to the housing is disengaged and the pivoting member is pivoted, in order to adjust a gap between the braking section and the drum to a desired value, the gap is adjusted by the adjusting unit and then the pivoting member is fastened to the housing by the fastening and releasing member. Thereby, it is possible to easily lengthen or shorten the gap. [0008] The braking device of an elevator hoist of the present invention preferably includes: a frictional member is provided on a surface of the a braking section; and a pressing correction unit to press the frictional member so that the frictional member is uniformly pressed to the drum when pressing the frictional member to the drum. In this braking device, the frictional member can be tightly pressed to the drum over its entire surface by the pressing correction unit. Accordingly, it is possible to increase the braking force of the braking device. [0009] The braking device of an elevator hoist of the present invention preferably includes: a rotatable drum; a braking section that is mounted to contact and separate from an outer peripheral surface of the drum; a drive section that presses the braking section to the outer peripheral surface of the drum and separates the braking section from the outer peripheral surface of the drum; a pivoting member to which the drive section is provided; a first attachment part that is adapted to pivotably mount one end of the pivoting member and is mounted around the drum; a second attachment part that is adapted to fasten and release the other end of the pivoting member and is mounted around the drum, and a distance adjusting unit that adjusts a distance between the other end of the pivoting member and the second attachment part, with the other end of the pivoting member being fastened to the second attachment part. [0010] According to the braking device, since the one end of the pivoting member is attached to the first attachment part so that it can be pivoted, a distance between the other end of the pivoting member and the second attachment part is changed as the pivoting member is pivoted. Based on the distance, a gap between the braking section and the drum is changed in the separated state of the braking section and the drum. Accordingly, it is possible to easily adjust the gap in the separated state of the braking section and the drum by adjusting the distance between the other end of the pivoting member and the second attachment part by the distance adjusting unit. [0011] According to the braking device for an elevator hoist of the present invention, preferably, the first attachment part has a hole, and the pivoting member has a hole at the one end, and the braking device includes a shaft member that is inserted into the hole of the first attachment part and the hole of the one end of the pivoting member. According to this braking device, when the fastened state is released to release the pivoting member from the second attachment part, the pivoting member is pivoted about the shaft member of the first attachment part serving as a supporting point. Accordingly, it is possible to pivot the pivoting member with the simple configuration. [0012] According to the braking device for an elevator hoist of the present invention, preferably, one of hole of the first attachment part and the hole of the one end of the pivoting member is a screw hole, and the shaft member is screw-threaded into the screw hole. According to this braking device, the one end of the pivoting member is fixed to the first attachment part by the screw-threaded shaft member and the other end of the pivoting member is fastened to the second attachment part. In addition, when the screw-threaded shaft member is slightly loosened and then the fastened state of the other end of the pivoting member is released, the pivoting member can be pivoted about the shaft member serving as a supporting point. Accordingly, since both ends of the pivoting member are securely fixed to the first attachment part and the second attachment part, it is possible to easily press the braking section to the outer peripheral surface of the drum. When maintaining the braking device, for example, it is possible to pivot or fix the pivoting member by loosening or tightening the screw thread engagement of the shaft member. Accordingly, it is possible to easily adjust the pivoting position of the pivoting member. [0013] According to the braking device for an elevator hoist of the present invention, preferably, the distance adjusting unit has a distance adjusting member having a thickness, and the other end of the pivoting member is fastened to the second attachment part via the distance adjusting member. According to this braking device, when the distance adjusting member having a thickness is sandwiched between the second attachment part and the other end of the pivoting member and fastened, the gap between the braking section and the drum with the braking section and the drum being separated is determined depending on the thickness of the distance adjusting member. Accordingly, it is possible to easily adjust the gap with the braking section and the drum being separated by adjusting the thickness of the distance adjusting member. [0014] According to the braking device for an elevator hoist of the present invention, preferably, two of distance adjusting members, of which thickness values differ from each other, are alternately disposed side by side in a rotating axis center direction of the drum. According to this braking device, when the two of distance adjusting members having different thickness are alternately disposed side by side in a rotating axis center direction of the drum between the second attachment part and the other end of the pivoting member, it is possible to uniformly adjust the gap between the braking section and the drum in the rotating axis center direction with the braking section and the drum being separated. [0015] According to the braking device for an elevator hoist of the present invention, preferably, the distance adjusting unit has: a hole that is provided to the other end of the pivoting member; a screw hole that is provided to the second attachment part a bolt that is inserted into the hole and is screw-threaded into the screw hole so that it can be moved forward-and-backward; a first nut that is screw-threaded on the bolt and is fixed on a surface of the other end of the pivoting member facing the second attachment parts; and a second nut that is screw-threaded on the bolt and fixes the bolt to the second attachment part. [0016] According to this braking device, when the distance between the other end of the pivoting member and the second attachment part is changed by tightening or loosening the bolt inserted into the hole of the other end of the pivoting member with the bolt being screw-threaded into the screw hole of the second attachment part, the gap between the braking section and the drum with the braking section and the drum being separated is changed depending on the distance. Then, the pivoting member is fixed to the bolt by the first nut and the bolt is fixed to the second attachment part by the second nut, so that the gap is fixed. Accordingly, since it is possible to continuously change the gap between the braking section and the drum with the braking section and the drum being separated by tightening or loosening the bolt, it is possible to easily adjust the gap. [0017] According to the braking device for an elevator hoist of the present invention, preferably, the braking device includes a pivot-preventing unit that prevents the pivoting member from being pivoted in a state in which the fastened state of the other end of the pivoting member to the second attachment part is released. According to this braking device, even when the fastened state of the other end of the pivoting member to the second attachment part is released, it is possible to prevent the pivoting member from being pivoted by the pivot-preventing unit. [0018] According to the braking device for an elevator hoist of the present invention, preferably, the drive section has a first elastic member that is provided to the pivoting member; an electromagnetic coil that is provided to the pivoting member; a movable iron core that urges the braking section to the outer peripheral surface of the drum by the first elastic member at a non-excitation state of the electromagnetic coil and separates the braking section from the outer peripheral surface of the drum against the urging force of the first elastic member at an excited state of the electromagnetic coil, a guide unit that slidingly guides the movement of the movable iron core. The guide unit has a first member that is fixed to the pivoting member and a second member that is provided around the first member and is elastically deformed more easily than the first member, and the movable iron core slidingly moves along the second member. [0019] The movable iron core slides along the second member that is provided around the first member fixed to the pivoting member and is easily elastically-deformed. Accordingly, since the movable iron core can flexibly change the posture thereof, it can slide without being caught at the first member. [0020] According to the braking device for an elevator hoist of the present invention, preferably, the guide unit the first member, which has a rod shape, fixed to a surface of the pivoting member facing the drum and has a first recess of a ring shape at a leading end thereof: and the second member, which has an elastic ring shape, fitted to the first recess and has a protrusion to slidingly guide the movement of the movable iron core. The movable iron core is provided with a concave portion into which the first member and the second member can be inserted. When the movable iron core is moved, an inner peripheral surface of the concave portion and the second member slide. [0021] The movable iron core slides along the second member having an elastic ring shape fitted in the first recess of the first member fixed to the pivoting member. Accordingly, since the movable iron core can flexibly change the posture thereof even when the axis center of the first member and the axis center of the concave portion of the movable iron core are deviated due to the manufacturing errors, the movable iron core can slide without being caught at the first member. [0022] According to the braking device for an elevator hoist of the present invention, preferably, the guide unit has: the first member, which has a rod shape, fixed to a surface of the pivoting member facing the drum and has a first recess of a ring shape at a leading end thereof; and the second member, which has an elastic ring shape, fitted to the first recess and has a protrusion to slidingly guide the movement of the movable iron core. The movable iron core is provided at four corners thereof with third circular recesses that can be engaged to the protrusions of the second members. When the movable iron core is moved, the second members slide along the third recesses. [0023] The movable iron core slides along the second members of an elastic ring shape fitted in the second recesses of the first members fixed to the pivoting member. Accordingly, since the movable iron core can flexibly change the posture thereof even when the axis centers of the first members and the axis centers of the third recesses of the movable iron core are deviated due to the manufacturing errors, the movable iron core can slide without being caught at the first members. [0024] According to the braking device for an elevator hoist of the present invention, preferably, the braking section has: a frictional member that is provided to face the outer peripheral surface of the drum; and a correction unit that is provided to uniformly press a braking surface of the frictional member to the outer peripheral surface of the drum and to uniform a gap between the braking surface of the frictional member and the outer peripheral surface of the drum. According to this braking device, when pressing the frictional member to the drum, the correction unit presses substantially and uniformly the braking surface of the frictional member to the outer peripheral surface of the drum. Thus, it is possible to secure the stable braking force. In addition, when separating the frictional member from the drum, the gap between the braking surface of the frictional member and the outer peripheral surface of the drum is substantially uniform. Thus, it is possible to easily adjust the gap into a prescribed value. [0025] According to the braking device for an elevator hoist of the present invention, preferably, the correction unit has: a spherical band seat that has a spherical band portion and a pillar portion contacting the movable iron core; a spherical crown seat that has a concave spherical crown portion to be engaged with the spherical band portion; a plate member that contacts the spherical crown seat and to which the frictional member is fixed; and a second elastic member that has a leading end communicating with a base portion, wherein the base portion is fixed to the movable iron core and the leading end presses the plate member to urge the plate member toward the movable iron core. A position at which the leading end of the second elastic member presses the plate member is near a virtual line that is formed as a virtual plane including a rotating axis center of the drum and a center of the spherical band portion of the spherical band seat intersects with a surface of the plate member facing the drum. [0026] According to this braking device, when the frictional member is pressed to the drum, the engaged position of the spherical band seat and the spherical crown seat is deviated, and the second elastic member is deformed. Thus, the directions of the frictional member and the plate member facing the outer peripheral surface of the drum are changed, and the braking surface of the frictional member is tightly contacted to the outer peripheral surface of the drum, so that the frictional member presses uniformly. In addition, although the second elastic member presses the plate member toward the movable iron core, the position at which the plate member is pressed is near the part at which the plate member is supported to the spherical band seat. Thus, the force by which the second elastic member changes the posture of the plate member is small. Therefore, even when the frictional member is separated from the drum, the plate member is separated from the drum with the substantially same posture as that in the pressed state. As a result, the gap between the frictional member and the drum is substantially uniform. Accordingly, it is possible to secure the stable braking force at the braking time. In addition, when the frictional member is separated from the drum, the gap is substantially uniform, so that it is possible to easily adjust the gap to the prescribed value. EFFECTS OF THE PRESENT INVENTION [0027] According to the present invention, it is possible to provide a braking device for an elevator hoist capable of easily adjusting a gap between a frictional member and a drum. BRIEF DESCRIPTION OF THE DRAWINGS [0028] [FIG. 1] It is an overall configuration view of a braking device for an elevator hoist according to an illustrative embodiment of the present invention. [FIG. 2] A view illustrates a state in which arms of the braking device shown in FIG. 1 are opened. [FIG. 3] As viewed from an arrow III-III direction of FIG 1, a view illustrates a state at the time of brake releasing. [FIG. 4] As viewed from an arrow IV-IV direction of FIG. 1, a view illustrates a state at the time of brake braking. [FIG. 5] It is an overall configuration view of a braking device for an elevator hoist according to another illustrative embodiment of the present invention. [FIG. 6] A view illustrates a state in which arms of the braking device according to another illustrative embodiment of the present invention are pivoted. [FIG. 7] It is a partially enlarged view of the braking device according to another illustrative embodiment of the present invention, and the view illustrates a state in which a drum is released. [FIG. 8] It is a partially enlarged view of the braking device according to another illustrative embodiment of the present invention, the view illustrates a state in which a drum is braked. [FIG. 9] As viewed from an arrow V direction of FIG. 5, a view illustrates a state in which a spacer is sandwiched at one location so as to adjust a gap. [FIG. 10] It is a view of another illustrative embodiment of the present invention, the view illustrates a state in which spacers are sandwiched side by side at two locations so as to adjust a gap. [FIG. 11] As viewed from an arrow VII direction of FIG. 6, a view illustrates a pivoting member, a drive section, a braking section and a guide unit. [FIG. 12] A view illustrates a pivoting member, a drive section, a braking section and a guide unit according to another illustrative embodiment of the present invention. [FIG. 13] As viewed from an arrow VI-VI direction of FIG. 5 according to another illustrative embodiment of the present invention, a view illustrates a pivoting member, a drive section and a braking section. [FIG. 14] It is a pictorial view illustrating a position at which an elastic clip of another illustrative embodiment of the present invention presses a shoe. [FIG. 15] A view illustrates another illustrative embodiment of the present invention, and the view illustrates a state in which a wedge-shaped spacer is sandwiched so as to adjust a distance. [FIG. 16] A view illustrates a configuration of a distance adjustment unit according to another illustrative embodiment of the present invention. [FIG. 17] It is an overall configuration view of another illustrative embodiment of the present invention. [FIG. 18] It is an overall configuration view of a braking device for an elevator hoist illustrating another illustrative embodiment of the present invention, and the view illustrates that arms are pivoted. DESCRIPTION OF PREFERRED ILLUSTRATIVE EMBODIMENTS [0029] First Illustrative Embodiment An illustrative embodiment of the present invention will be described with reference to FIGS. 1 to 4. FIG. 1 is an overall configuration view of a braking device for an elevator hoist according to an illustrative embodiment of the present invention. FIG. 2 is a view illustrating a state in which arms of the braking device shown in FIG. 1 are opened. FIG. 3 is a view seen from an arrow III-III direction of FIG. 1, illustrating a state at the time of brake releasing. FIG. 4 is a view seen from an arrow IV-IV direction of FIG. 1, illustrating a state at the time of brake braking. In FIG. 1, a braking device 1 for an elevator hoist is symmetrically formed in the left-right direction while sandwiching a drum 5. The braking device 1 includes the rotatable drum 5 coupled to a rotor of a motor and a housing 7 that accommodates the drum 5 therein and has opening sections 7a, which has one end and the other end, opened at both sides. The braking device 1 has arms 11 as pivoting member and braking drive sections 30, which is provided to the arms 11, to press and separate frictional members 69 to and from an outer peripheral surface of the drum 5. [0030] The arm 11 is pivotably coupled to one end of the opening section 7a of the housing 7 by a pin 9, and the arm 11 is coupled and fixed to the other end of the opening section 7a of the housing via a spacer 15 as an adjustment unit for adjusting a distance by a bolt 13 as a fastening and opening member. In addition, as the adjustment unit, a jack bolt may be provided to a screw hole formed at the other end portion of the arm 11, instead of the spacer 15. In the meantime, the arm 11, the spacer 15, the bolt 13, the pin 9 and the braking drive section 30 are respectively provided one by one to right and left sides. [0031] A gap between the frictional member 69 and the drum 5 is changed depending on a thickness of the spacer 15. A distance X from the pin 9 that is a pivoting center of the arm 11 to the fastening part of the bolt 13 is greater than a distance Y from the pin 9 to a center of a longitudinal direction of the arm 11. When a change amount of a thickness of the spacer is expressed with Aa and a change amount of the gap b is expressed with Ab, a following relation is satisfied. Ab = Aa x (Y/X) Accordingly, since Y < X is satisfied, Ab < Aa is satisfied. Hence, the braking device 1 is formed so that the gap b can be easily and finely adjusted depending on the thickness a of the spacer 15. [0032] In FIG. 3, the braking drive section 30 is provided to the arm 11 and has a braking section 50 that brakes the drum 5 and a drive section 70 having a movable iron core 72 that translationally moves the braking section 50 and presses and separates one end surface of the braking section 50 to and from the outer peripheral surface of the drum 5. The braking section 50 is coupled and fixed to the movable iron core 72 and has a pressing correction section 60 as a pressing correction unit and the frictional member 69 that is fixed on a surface of the pressing correction section 60 facing the drum 5. Since a non-uniform gap is formed due to the manufacturing errors between the frictional member 69 and the drum 5 in the opened state of the braking device 1, the pressing correction section 60 is provided so as to uniformly press the frictional member 69 and the drum 5 in the braking state of the braking device 1. [0033] In FIG. 3, the pressing correction section 60 is fixed to the movable iron core 72 and has a spherical band seat 62 that has a spherical band portion, a concave spherical seat 64 having a concave portion that is engaged with the spherical band portion of the spherical band seat 62, and a brake shoe 66 that is fixed on a planar side of the concave spherical seat 64. In addition, the pressing correction section 60 has Z-shaped elastic clips 68 that press the brake shoe 66 toward the spherical band seat 62 and are fixed to the movable iron core 72 by screws 67 and the frictional member 69 that is fixed on a surface of the brake shoe 66 facing the drum 5. [0034] In FIG. 3, the drive section 70 has the movable iron core 72 that is provided on a surface of the arm 11 facing the drum 5, springs 74 that urge the movable iron core 72 toward the drum 5 and is mounted to the arm 11, and electromagnetic coils 76 that suck the movable iron core 72 toward the arm 11 against the force of the springs 74. [0035] First, the operation of the braking device configured as described above will be described with reference to FIGS. 1, 3 and 4. In order to release the drum 5 of the braking device 1, when the electromagnetic coils 76 are excited by enabling the current to flow, the movable iron cores 72 are sucked toward the arms 11, so that the gaps b are formed between the frictional members 69 and the drum 5. As the gaps b are formed, the drum 5 can smoothly rotate. [0036] Then, in order to brake the drum 5, when the electromagnetic coils 76 are under non-excited state by cutting off the current of the electromagnetic coils 76, the springs 74 are extended to urge the movable iron cores 72 toward the drum 72, so that the frictional members 69 are pressed to the drum 5, as shown in FIG. 4. At this time, the engaged positions of the spherical band seats 62 and the concave spherical seats 64 of the pressing correction sections 60 are deviated to elastically deform the elastic clips 68. As a result, the frictional members 69 are tightly pressed to the drum 5 over the entire surface thereof. After that, when the electromagnetic coils 76 are excited, the movable iron cores 72 are sucked toward the arms 11 to release the drum 5 of the braking device 1 and the spherical band seats 62 and the concave spherical seats 64 are returned to the engaged positions by restoring force of the elastic clips 68. [0037] In the below, the gap adjustment between the braking section 50 and the drum 5 of the braking device 1 will be described with reference to FIGS. 1, 2 and 3. After a maintenance-man measures the gap b, the maintenance-man removes the bolt 13 fastened to the housing 7 to pivot the arm 11 about the pin 9 serving as a support point in the arrow A direction, as shown in FIG. 2. In order to adjust the gap b to a desired value, the maintenance-man replaces a spacer 15 having a predetermined thickness prepared in advance and again fastens the arm 11 to the housing 7 by the bolt 13. Thereby, by thickening or thinning the thickness of the spacer 15, it is possible to lengthen or shorten the distance of the gap b. In the meantime, the spacer 15 may be singular or plural. [0038] When replacing the frictional member 69 of the braking device 1, the arm 11 is pivoted as shown in FIG. 2. At that state, the screw 67 of the braking section 60 is removed, the elastic clips 68 are detached, the brake shoe 66 is detached and a new brake shoe 66 is attached. Since it is possible to secure a wide operation space, it is possible to easily replace the brake shoe 66 and the like. [0039] The braking device 1 for an elevator hoist configured as described above includes the housing 7 that accommodates the rotatable drum 5 therein and has the opened opening sections 7a, the arms 11 each of which is pivotably attached to one end of the opening section 7a and has the other end opened, the bolts 13 each of which fastens and releases the other end portion of the arm 11 to and from the other end of the opening section 7a, the spacers 15 each of which is adapted to adjust the distance between the other end portion of the arm 11 and the other end of the opening section with each spacer 15 being fastened to each arm 11 and the braking drive sections 30 that are provided to the arms 11 and press and separate the braking sections 50 to and from the outer peripheral surface of the drum 5. [0040] According to the braking device 1 configured as described above, in the state in which the bolts 13 fastened to the housing 7 are removed and then the arms 11 are pivoted about the pins 9 serving as support points in the arrow A direction, as shown in FIG. 2, in order to adjust the gaps b to a desired value, the spacers 15 are replaced with the spacers 15 having a predetermined thickness prepared in advance and then the arms 11 are again fastened to the housing 7 by the bolts 13. Thereby, by thickening or thinning the thickness of the spacer 15, it is possible to lengthen or shorten the distance of the gap b. In other words, by changing the thickness of the spacer 15, it is possible to easily adjust the gap b. [0041] In addition, the braking device 1 has the pressing correction section 60 that causes the frictional member 60 of the braking section 50 to be uniformly pressed on the drum 5 when pressing the braking section 50 to the drum 5. Thereby, since the frictional member 69 of the brake shoe 66 is coupled to the movable iron core 72 via the pressing corrosion section 60, it is possible to tightly press the drum 5 over its entire surface at the braking time without the influence by the manufacturing errors. Accordingly, it is possible to increase the braking force of the braking device 1. [0042] In the meantime, the arm 11 as a pivoting member is coupled and fixed to the other end of the opening section 7a of the housing 7 via the spacer 15 by the bolt 13 as a fastening and releasing member. However, by detaching the bolt 13 to release the arm 11 from the other end of the opening section 7a of the housing 7, the arm is opened with the spacer 15 having a predetermined thickness to be sandwiched. [0043] Second Illustrative Embodiment A second illustrative embodiment of the present invention will be described with reference to FIG. 17. A hoist 182 is mounted in a machine room 181 that is provided at the upper of a hoistway 180. The hoist 182 is provided with a sheave 183 and a braking device 101, and a drum 105 of the braking device 101 and the sheave 183 are integrally rotated by an electromotor. A rope 184 is wound on the sheave 183. A cage 185 is coupled to one end of the rope 184 and a balance weight 186 is coupled to the other end thereof. When the drum 105 of the braking device 101 is released and the sheave 183 is rotated, the cage 185 and the balance weight 186 are moved up and down. When the drum 105 of the braking device 101 is braked, the sheave 183 is stopped, so that the cage 185 and the balance weight 186 are stopped. [0044] FIG. 5 is an overall configuration view of the braking device 101 for the elevator hoist 182. FIG. 6 illustrates a state in which arms 111 as pivoting members of the braking device 101 for the elevator hoist 182, are pivoted. In the braking device 101, the drum 105 is rotatably provided to a holder 103. At both sides of the outer circumference of the drum 105, which are the surrounding area of the drum 105, attachment parts 103a as a first attachment part and attachment part 103b as a second attachment part are provided to the holder 103. The arms 111 are provided at both sides of the drum 105 facing to the outer peripheral surface, which is the braking surface of the drum 105. One end portion of the arm 111 is pivotably mounted to the attachment part 103 a and the other end portion is provided to the attachment part 103 b via a spacer 115 as a distance adjusting member. A surface of the arm 111 facing the drum 105 is provided with a drive section 170. A surface of the drive section 170 facing the drum 105 is provided with a braking section 150. [0045] The braking section 150 is provided with a frictional member 169 via a correction section 161 as a correction unit, and a shoe 166 as a plate member. A braking surface of the frictional member 169 is pressed and separated to and from the outer peripheral surface of the drum 105 by the drive section 170. [0046] FIG. 9 is a view seen from an arrow V direction of FIG. 5. A bolt 112 as a shaft member is inserted into a hole Ilia provided to one end portion of the arm 111 and is then screw-threaded into a screw hole 103c provided to the attachment part 103a, so that the arm 111 is fixed to the attachment part 103a. Also, as shown in FIG. 5, the other end portion of the arm 111 is fixed to the attachment part 103b via the spacer 115 having a thickness t by a bolt 113. A hook 117 as a pivot-preventing unit holds the other end portion of the arm 111 through the bolt 113 so that the arm 111 is not pivoted about the bolt 112 serving as a support point. Here, in order to pivot the arm 111, when a bolt 114, the hook 117 and the bolt 113 are taken off and the bolt 112 is loosened without falling out, the arm 111 can be pivoted about the bolt 112 serving as a support point, as shown in FIG. 6. [0047] In FIG. 5, the arm 111 can be pivoted about the bolt 112 serving as a support point. Accordingly, when the thickness t of the spacer 115 is changed, the gap g between the frictional member 169 and the drum 105 is changed depending on the thickness t of the spacer 115. In addition, regarding a distance XI between the bolt 112 that is a pivoting center of the arm 111 and the fastening part of the bolt 113 having sandwiched the spacer 113 and a distance Yl between the bolt 112 and the center of the frictional member 160, XI is set to be longer than Yl. [0048] When a change amount of the thickness t of the spacer 115 is expressed with dt and a change amount of the gap g is expressed with dg, a following relation is satisfied. dg = dt x (Yl / XI). Here, since YKX1 is satisfied, dg